Index: includes/bootstrap.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/bootstrap.inc,v
retrieving revision 1.389
diff -u -p -r1.389 bootstrap.inc
--- includes/bootstrap.inc	18 May 2010 18:33:30 -0000	1.389
+++ includes/bootstrap.inc	20 May 2010 05:37:37 -0000
@@ -2076,7 +2076,20 @@ function _drupal_bootstrap_page_cache() 
       exit;
     }
     else {
-      header('X-Drupal-Cache: MISS');
+      // Cache miss. Avoid a stampede.
+      require_once DRUPAL_ROOT . '/' . variable_get('lock_inc', 'includes/lock.inc');
+      lock_initialize();
+      $name = $GLOBALS['base_root'] . request_uri();
+      if (!lock_acquire($name, 1)) {
+        // Some other request is building cache. Wait, then re-run this function.
+        header('X-Drupal-Cache: WAIT');
+        lock_wait($name);
+        return _drupal_bootstrap_page_cache();
+      }
+      else {
+        // Proceed with page build;  cache its result, then release the lock.
+        header('X-Drupal-Cache: MISS');
+      }
     }
   }
 }
Index: includes/cache.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/cache.inc,v
retrieving revision 1.48
diff -u -p -r1.48 cache.inc
--- includes/cache.inc	18 May 2010 18:26:30 -0000	1.48
+++ includes/cache.inc	20 May 2010 05:37:37 -0000
@@ -421,6 +421,9 @@ class DrupalDatabaseCache implements Dru
         ->key(array('cid' => $cid))
         ->fields($fields)
         ->execute();
+      if ($this->bin == 'cache_page') {
+        file_put_contents('/tmp/cache.txt', $this->bin . "\n", FILE_APPEND);
+      }
     }
     catch (Exception $e) {
       // The database may not be available, so we'll ignore cache_set requests.
Index: includes/common.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/common.inc,v
retrieving revision 1.1168
diff -u -p -r1.1168 common.inc
--- includes/common.inc	19 May 2010 19:22:24 -0000	1.1168
+++ includes/common.inc	20 May 2010 05:37:39 -0000
@@ -4544,6 +4544,7 @@ function drupal_page_set_cache() {
         $cache->data['body'] = gzencode($cache->data['body'], 9, FORCE_GZIP);
       }
       cache_set($cache->cid, $cache->data, 'cache_page', $cache->expire);
+      lock_release($cache->cid);
     }
     return $cache;
   }
@@ -5187,7 +5188,7 @@ function drupal_render_cache_get($elemen
   }
   $bin = isset($elements['#cache']['bin']) ? $elements['#cache']['bin'] : 'cache';
 
-  if (!empty($cid) && $cache = cache_get($cid, $bin)) {
+  if ($cache = cache_get($cid, $bin)) {
     // Add additional libraries, JavaScript, CSS and other data attached
     // to this element.
     if (isset($cache->data['#attached'])) {
@@ -5196,7 +5197,18 @@ function drupal_render_cache_get($elemen
     // Return the rendered output.
     return $cache->data['#markup'];
   }
-  return FALSE;
+  else {
+    // Cache miss. Avoid a stampede.
+    if (!lock_acquire($cid, 1)) {
+      // Some other request is building cache. Wait, then re-run this function.
+      lock_wait($cid);
+      return drupal_render_cache_get($elements);
+    }
+    else {
+      // Proceed with rendering, cache the result, and then release the lock.
+      return FALSE;
+    }
+  }
 }
 
 /**
@@ -5232,6 +5244,7 @@ function drupal_render_cache_set(&$marku
   $bin = isset($elements['#cache']['bin']) ? $elements['#cache']['bin'] : 'cache';
   $expire = isset($elements['#cache']['expire']) ? $elements['#cache']['expire'] : CACHE_PERMANENT;
   cache_set($cid, $data, $bin, $expire);
+  lock_release($cid);
 }
 
 /**
Index: includes/lock.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/lock.inc,v
retrieving revision 1.4
diff -u -p -r1.4 lock.inc
--- includes/lock.inc	6 May 2010 15:20:18 -0000	1.4
+++ includes/lock.inc	20 May 2010 05:37:39 -0000
@@ -198,8 +198,9 @@ function lock_wait($name, $delay = 30) {
   while ($delay--) {
     // This function should only be called by a request that failed to get a
     // lock, so we sleep first to give the parallel request a chance to finish
-    // and release the lock.
-    sleep(1);
+    // and release the lock. Use usleep for 100ms, instead of sleep(1),  so that
+    // processes don't wait around too much longer than necessary.
+    usleep(100000);
     if (lock_may_be_available($name)) {
       // No longer need to wait.
       return FALSE;